Rotating multiple objects in animation
See that pretty record button by the keys at the bottom of the screen? Click that button. That's the Automatic Keyframe Button. 

You also want to open up the action editor to actually see the keyframes.

So open up that editor, select all of the blades. Press, I, which iirc is insert keyframe. It should insert a keyframe for all of the blades, if not, you will just need to do it individually. This will make blender store the pose for those different blades at that frame in time. Now all you need to do to animate is go to a different point in time, and just rotate all of the blades. You can do them all at the same time if you've shift selected them before rotating, and you have 'individual center' selected for the transform origin, which is what you seem to have set, judging by the two circles between your shading and widget option.

You can extrapolate on the animation, which will make Blender continue the animation that you already started, further down the timeline. You can also just duplicate the keyframes of the final position of the blade, drag it to say, +60 frames, then at +30 frames, insert another keyframe where it's 50% of the animation to cause it to loop. You can also edit the curve of the animation in the IPO editor.

If you have any more questions, feel free to comment on this answer.